The present invention relates generally to planar transformers used in soft switching and resonant power converters, and more particularly, to an integrated planar transformer and inductor assembly for use in soft switching and resonant power converters.
FIG. 1 illustrates a typical conventional planar transformer 10 used in soft switching and resonant power converters in which the inductive element of the resonant circuit is connected in parallel with a transformer. In such circuits, it is convenient to use the magnetizing inductance of the transformer 10 as the inductive element of the resonant circuit. Such conventional planar transformers 10 typically have a core 11 with a central gap 12 that surrounds planar interleaved primary and secondary windings 13, 14 or layers. The gap thickness is set to yield the necessary value of the magnetizing inductance for proper circuit operation. The interleaved primary and secondary rings 13, 14 are separated by insulating (dielectric) layers 15.
In such conventional planar transformers, the magnetizing (inductor) current in the secondary winding 14 crowds to the inside of the winding (current crowding 16), mostly within one skin depth of the innermost path in the planar structure of the planar transformer 10. This greatly increases the loss caused by the inductor current, due to the limited cross section carrying current.
Accordingly, it is an objective of the present invention to provide for an improved integrated planar transformer and inductor assembly for use in soft switching and resonant power converters that overcomes the limitations of conventional planar transformers by reducing the additional loss caused by the inductor current.